CVE-2026-19487: Perl versions from 5.9.4 before 5.41.9 produce incorrect regular expression match results when a stale failure flag ends the Aho-Corasick prescan early in S_find_byclass

mediumCVSS 5.3CVE-2026-19487

CSIRTS triage

vendor: Perl product: PerlOtheraffected: 5.9.4 to <5.41.9

What: Regular expression match results are incorrect when a stale failure flag prematurely ends Aho-Corasick prescan in S_find_byclass.
Who is affected: Perl versions from 5.9.4 through 5.41.8 are affected.
Urgency: Medium priority; regex incorrectness can cause unexpected behavior in pattern matching.
Action: Upgrade to Perl 5.41.9 or later.

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Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: medium — CVSS 5.3
Published: 2026-08-11
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-19487

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-194870.43% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 36% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-19487	coverage & exploitation status	NVD · CVE.org

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